“Why do ordinary incandescent bulbs operate at far below normal voltages and emit yellowish light?”


It is the very working principle of these lamps that does this. The LEDs emit light by the electronic excitation, so in a red LED of 20 mA, whether the current is 1 mA or 20 mA, the excitation of the atoms causes it to always emit light of the same color: red. With the fluorescent and electronic lamps the same occurs. Whether the current, if there is ionization, the light emitted depends only on the phosphorus that produces it in white (or other) color. For incandescent lamps the color of light is determined by the heating of the filament according to Boltzman's law. By this law, the higher the temperature, starting from the infrared, the predominant light tends towards the blue. Thus, when it is very cold the light begins in the infrared, it changes to red, orange, yellow, then reaches the white (mixing the colors of the spectrum) and then, if the heating is too much it can turn blue. But to get to that bluish light the temperature of the filament will be at the limit and it will burn right away.




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